Details up front: method section · TFC.
I have the document in front of me and I can read the numbers. What I cannot do is interpret them.
I am reasonably comfortable with statistics and completely uncomfortable with chromatography, or vice versa.
What is the correct interpretation, and what is the common misreading?
Before anything else, check that the lot number on the certificate matches the vial in your hand — that traces back to your material and not to some other lot from some other date.
The test date matters because a certificate six months older than the vial is not evidence about your material, it is evidence about what the material was like half a year ago.
| Δ mass (Da) | Most likely cause | Distinguishing feature |
|---|---|---|
| +1 | Deamidation (Asn or Gln) | New peak, slightly earlier retention |
| −17 | Loss of ammonia | Often with deamidation |
| −18 | Dehydration / succinimide | pH-dependent, reversible |
| +16 | Oxidation (Met, Trp) | Earlier retention, light-related |
| −128 | Missing Gln or Lys | Deletion sequence from synthesis |
| 0 | Isomer: racemisation or scrambling | Same mass, shifted retention |
To be exact about it, a purity figure to two decimal places with no supporting chromatogram is giving false precision and is a red flag on the same level as spelling errors.
Published inter-laboratory comparisons of the same material routinely find spreads of half a per cent to a full per cent, which sets realistic expectations.
The practical summary: check the lot number, ask for the method, and reserve judgement until you have both.
edited 28 Apr 2026 by tobias_maartens — added the placebo-arm figures
Aggregated, published test results and vendor ratings built from submitted batches. Methodology stated, dataset browsable, no listing fees.
Browse resultsA useful certificate has five elements: the lot number, the analytical method, the reported result with units, the date of analysis, and the primary data or a reference to it.
Writing the lot number on your vial in permanent marker is worth doing because it later proves that the certificate traces to your material.
Specifically, the laboratory name and accreditation status can be checked in real time against the testing service's own register, and that two-minute check catches substituted certificates.
Industry guidance on this topic is consistent because it comes from first principles rather than convention.
My working rule is that a document without a lot number, a method section and a test date is marketing.
Worth being precise here: what a useful certificate carries is debatable, but there are certain fields that almost no research-grade certificate includes despite their being standard in pharmaceutical work.
The certificate is a snapshot and nothing else — it tells you about the material on one day from one sample of one lot, and extrapolation beyond that requires logic.
The relevant detail is that multiple testing on the same lot reported in a single document suggests internal quality control; identical figures across different lots suggests the same certificate reused.
The standards that exist in this space — ICH Q3A, Q3B and various pharmacopoeial chapters — are worth reading once even if nothing you test is obliged to meet them.
If the certificate does not trace to your vial, it is not evidence about your vial.
Ask PeptideStack is a static archive. Posting is closed, but the norms are worth stating: answer the question that was asked, show your working, cite the trial or the certificate, and say plainly where the evidence runs out.